The present invention relates generally to implantable medical devices and, more particularly, to implantable pacemakers and cardioverter-defibrillators for detecting and treating atrial and ventricular tachyarrhythmias.
Implantable cardioverter-defibrillators (ICDs) have been developed that employ detection algorithms capable of recognizing and treating ventricular tachycardias and ventricular fibrillation. Detection algorithms are also being developed to recognize and treat atrial tachycardias and atrial fibrillation. In general, ICDs are designed to treat such tachycardias with antitachycardia pacing and low-energy cardioversion shocks in conjunction with back-up defibrillation therapy. These ICDs monitor the heart rate and the onset of the arrhythmia by sensing endocardial signals and determining when the heart is in need of either cardioversion to treat a given tachycardia or of defibrillation to treat a fibrillation condition.
Certain ICDs have been designed with dual chamber sensing capabilities to detect and analyze both ventricular and atrial endocardial signals. This increase in cardiac signal input to the ICD has provided an opportunity to determine the origin and the nature of atrial and ventricular tachyarrhythmia, and to reduce the frequency of inappropriate therapy being delivered to an implant patient.
However, while the combination of antitachycardia pacing with low and high energy shock delivery, as well as backup bradycardia pacing, in ICDs has expanded the number of clinical situations in which the device may appropriately be employed, improved means of coordinating ventricular and atrial rate information in a way that results in a system that effectively and efficiently treats ventricular and atrial tachyarrhythmias is still desired.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading the present specification, there is a need in the art for improved atrial and ventricular arrhythmia detection techniques. There exists a further need for such techniques that provide for preferential detection and treatment of ventricular arrhythmias relative to atrial arrhythmias. The present invention fulfills these and other needs.
The present invention is directed to systems and methods for detecting arrhythmias. One embodiment of the present invention provides for improved atrial tachyarrhythmia detection. Another embodiment of the present invention provides for improved atrial and ventricular tachyarrhythmia detection. In an embodiment which provides for concurrent detection of atrial and ventricular tachyarrhythmia, the detection methodology provides for increased sensitivity and response to ventricular tachyarrhythmia detection relative to atrial tachyarrhythmia detection and response sensitivity.
An arrhythmia detection methodology of the present invention is preferably implemented with an implantable medical device, such as devices that provide for one or a combination of pacing, cardioverting, defibrillating, and re-synchronizing functions. According to one embodiment, atrial and ventricular interval rates are developed from sensed atrial and ventricular events, respectively. Atrial interval rates are classified in an atrial window. The atrial window is defined to have a first length and a first satisfaction criterion. The atrial interval rates in the atrial window are typically classified as fast or slow with respect to a predefined threshold.
Ventricular interval rates are classified in a ventricular window. The ventricular window is defined to have a second length and a second satisfaction criterion. The second length of the ventricular window differs from the first length of the atrial window so as to enhance detection of ventricular arrhythmias relative to atrial arrhythmia detection. The ventricular interval rates in the ventricular window are typically classified as fast or slow.
A ventricular episode is declared in response to satisfying the ventricular window by comparing classified ventricular interval rates to the second satisfaction criterion. An atrial episode is declared in response to satisfying the atrial window by comparing classified atrial interval rates to the first satisfaction criterion. One or more additional detection or verification operations may be performed to verify continuance of a sustained, rather than transitory, ventricular arrhythmia condition. One or more additional detection or verification operations may be performed to verify continuance of a sustained, rather than transitory, atrial arrhythmia condition.
In one embodiment, a plurality of atrial and ventricular windows are operative with respect to each of a plurality of rate zones. In such a configuration, each of the developing, classifying, and declaring processes are operative with respect to each of the plurality of rate zones.
In accordance with another embodiment of the present invention, atrial and ventricular interval rates are developed from sensed atrial and ventricular events, respectively. An atrial window having a first length and a first satisfaction criterion is provided. A ventricular window having a second length and a second satisfaction criterion is also provided. The second length of the ventricular window differs from the first length of the atrial window to enhance detection of ventricular arrhythmias relative to atrial arrhythmia detection. Operations are performed to determine if the atrial and ventricular windows are satisfied according to the first and second satisfaction criteria, respectively.
The detection methodology according to this embodiment provides for determining, in response to satisfaction of the ventricular window, whether ventricular arrhythmia therapy is to be initiated. The detection methodology further provides for determining, in response to satisfaction of the atrial window and non-initiation of ventricular arrhythmia therapy, whether atrial arrhythmia therapy is to be initiated.
Atrial arrhythmia therapy is inhibited or delayed under several scenarios. Atrial arrhythmia therapy is inhibited or delayed during a time period in which initiation of ventricular arrhythmia therapy is being determined. Inhibiting or delaying the atrial arrhythmia therapy also occurs if the atrial and ventricular interval rates are substantially equal. Atrial arrhythmia therapy is inhibited or delayed if an average of the ventricular interval rates is greater than an average of the atrial interval rates. Inhibiting or delaying atrial arrhythmia therapy is also effected if a representative atrial rate developed from the atrial interval rates fails to exceed a representative ventricular rate developed from the ventricular interval rates by at least a predetermined factor. For example, atrial arrhythmia therapy is inhibited or delayed if an average or median of the atrial interval rates fails to exceed an average or median of the ventricular interval rates by at least a predetermined factor.
In accordance with yet another embodiment of the present invention, a body implantable system for detecting atrial and/or ventricular arrhythmia includes at least one lead comprising atrial and ventricular electrodes. A detector is coupled to the lead, and senses atrial events and ventricular events. Memory is configured to define an atrial window having a first length and a first satisfaction criterion. The memory is also configured to define a ventricular window having a second length and a second satisfaction criterion. The second length of the ventricular window differs from the first length of the atrial window to enhance detection of ventricular arrhythmias relative to atrial arrhythmia detection.
A control circuit is coupled to the detector and memory. The control circuit classifies atrial and ventricular interval rates in the atrial and ventricular windows, respectively. The control circuit declares a ventricular episode in response to satisfying the ventricular window by comparing classified ventricular interval rates to the second satisfaction criterion. The control circuit also declares an atrial episode in response to satisfying the atrial window by comparing classified atrial interval rates to the first satisfaction criterion. The control circuit inhibits atrial arrhythmia therapy under several scenarios, such as those discussed hereinabove.
In accordance with systems and methods of the present invention, the first length of the atrial window is greater than the second length of the ventricular window. For example, the first length of the atrial window length may be between two times and four times the second length of the ventricular window. By way of further example, the first length of the atrial window may be at least four times greater than the second length of the ventricular window.
The first satisfaction criterion associated with the atrial window is typically different from the second satisfaction criterion associated with the ventricular window. Alternatively, the first and second satisfaction criteria may be the same. Each of the first and second satisfaction criterion may represent a predetermined number, a predetermined percentage or a predetermined ratio of the classified atrial and ventricular interval rates relative to the first and second lengths. For example, the first satisfaction criterion may represent a predetermined number, percentage or ratio of the atrial interval rates classified as fast atrial interval rates relative to the first length. The second satisfaction criterion, in this case, represents a predetermined number or percentage of the ventricular interval rates classified as fast ventricular interval rates relative to the second length.
By way of particular example, the first satisfaction criterion may represent 32 of 40 (or 80 percent) of the atrial interval rates classified as fast atrial interval rates in the atrial detection window. The second satisfaction criterion, according to this example, may also represent 8 of 10 (or 80 percent) of the ventricular interval rates classified as fast ventricular interval rates in the ventricular detection window.
According to another embodiment, an atrial episode is verified as being a sustained atrial episode in response to satisfaction of the atrial window by a third satisfaction criterion for subsequent atrial interval rates. Each of the first and third satisfaction criterion may, for example, represent a predetermined number, percentage or ratio of the atrial interval rates classified as fast atrial interval rates relative to the first length, and the third satisfaction criterion is less than the first satisfaction criterion. The first satisfaction criterion, according to one approach, represents about 80 percent of the atrial interval rates classified as fast atrial interval rates and the third satisfaction criterion represents about 60 percent of the subsequent atrial interval rates classified as fast atrial interval rates.
A ventricular episode, according to this embodiment, is verified as being a sustained ventricular episode in response to the ventricular window being satisfied by a fourth satisfaction criterion for subsequent ventricular interval rates. Each of the second and fourth satisfaction criterion represents a predetermined number, percentage or ratio of the ventricular interval rates classified as fast ventricular interval rates relative to the second length, and the fourth satisfaction criterion is less than the second satisfaction criterion. For example, the second satisfaction criterion may represent about 80 percent of the ventricular interval rates classified as fast ventricular interval rates and the fourth satisfaction criterion may represent about 60 percent of the subsequent ventricular interval rates classified as fast ventricular interval rates.
The above summary of the present invention is not intended to describe each embodiment or every implementation of the present invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.